A magneto-optical disk memory has come in practice as a rewritable optical disk memory. Information can be rewritten with respect to the magneto-optical disk memory such that an old information is erased and thereafter a new information is recorded there.
According to a magnetic field modulated overwriting, it is not necessary to erase the old information, thereby enabling to rewrite the information at a high speed. However, the rewriting has the following drawbacks. More specifically, it is difficult to modulate the magnetic field at high frequencys. Further, in order to apply the high frequency magnetic field having a magnitude enough to overwrite, it is required that a magnetic field generating mechanism be in close proximity to the magneto-optical disk memory.
In order to overcome the foregoing drawbacks, the following optically modulated overwriting method is proposed in a Japanese unexamined patent publication No. 62-175948. According to the method, a magneto-optical medium having double layers structure, i.e., a recording layer and an auxiliary recording layer, is employed and the overwriting is carried out based on the modulation of the laser power. With the arrangement, the high frequency magnetic field is no required, so that the overwriting can be carried out at more high speed.
However, the above-mentioned conventional structure has the following problems. More specifically, a magnetization direction of the auxiliary recording layer is preliminarily completed so as to have one direction for each overwriting. So, an initialization magnetic field generating mechanism should be provided in addition to the recording magnetic field generating mechanism, thereby resulting in presenting a large-sized recording and reproducing apparatus and thereby resulting in increasing the cost for the manufacturing.